This invention relates to TOW missile systems and, more particularly, to an improved system for locating a target within the TOW missile's target acquisition sensor's field of view.
Current TOW missile systems use a xenon beacon incorporated within the missile as a way of locating the beacon's (and hence the missile's) position. For target tracking and missile guidance purposes, the missile's position is located within the system's target acquisition sensor's field of view. The sensor is typically a xenon beacon tracker (XBT). Recent improvements in TOW missile systems include, for example, a new tracker which allows the user to simultaneously view both the missile and the target, this being done in the long infrared portion (8-12 microns) of the light spectrum. This improvement is shown and discussed in U.S. Pat. No. 5,062,586 which is assigned to the same assignee as the present invention. These systems are limited in that the xenon beacon tracker only sees the beacon. It does not see the target. Consequently, the tracker is boresighted with a television camera, or forward looking infrared receiver (FLIR). The FLIR, which is also part of the tracking system, can see the target. If the beacon tracker and FLIR are not boresighted, tracking errors may develop which could cause the missile to miss its target. It would therefore be advantageous to have a single sensor capable of seeing both the target and the xenon beacon simultaneously, since this would alleviate the need for boresighting the two separate sensors.
In the newer tracking systems there is a trend to remove hard optics from the system. One reason for this is a growing concern over laser hardness and safety. Using a single sensor capable of both visually sighting a target and tracking a xenon beacon, creates additional system advantages. Conventional detection arrays of charge coupled devices (CCD's), CID's, and even tube cameras, have their sensitivity extended so they can work in the near infrared (IR) portion of the light spectrum. Similarly, medium range IR sensors; i.e., those operating in the range of 3-5 microns, can have their range extended toward the lower, longer visible wavelength end of the spectrum. Now, they can also sense the near IR signature of a xenon beacon.
A xenon beacon is identifiable by a high-frequency modulation. Sensing this modulation helps distinguish the beacon from countermeasures such as decoys or flares used by an enemy. Currently available sensors have frame rates of 30 Hz., and field rates of 60 Hz., for example, there being two scans per frame. Photosensitive diodes such as those used in CCD or CID cameras, or in starring focal plane cameras, have a 1 MHz., or greater, intrinsic bandwidth. While scanning and addressing these diodes produces the 30 Hz. frame rate; in diode arrays, local addressing rates can exceed 1 MHz. The problem heretofore has been the ability to achieve this high frequency operation in a sensor operating in this 30-60 Hz. frequency range.
A further consideration with respect to these prior art systems and their problems is one of target detection and recognition. Target detection means sensing that something is in the sensor's field of view; while target recognition is determining what it is. In battlefield situations, the ability to spot a potential threat at the farthest possible range and immediately identify it as a threat or otherwise cannot be understated.